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By Gabe Gutierrez and Bianca Seward

McALLEN, Texas — Griselda Vásquez Mejía, a mother detained on the U.S.-Mexico border, was told the day her son was taken away that the two would be together again in 48 hours. It's been 10 days.

The separation has been agonizing for Vásquez, who has remained at the Port Isabel Detention Center near Brownsville at the most southern tip of Texas.

“It’s really difficult and very sad,” she told NBC News by phone from inside the detention center. Vásquez said that she had made the decision to cross the Rio Grande illegally because of the violence and poverty in her home country of Honduras.

She never expected that her son would be taken away — and that information about him would be so tough to get.

“They haven’t told us anything,” she said.

NBC News spoke by phone with four mothers in detention, including Vásquez, who had similar stories. Provided phone cards by their attorney, they described in their calls a roughly two-week trek through Central America and Mexico that ended when U.S. immigration agents picked them up after they crossed the border illegally.

The mothers all said they were applying for asylum, but were devastated to learn that their children would be taken from them.

President Donald Trump signed an executive order Wednesday ending the forced separations of children from parents so that the parents could be prosecuted for illegal entry. The government had been separating families for months, splitting more than 2,300 children from parents or guardians. Some have been sent across the country to shelters and foster care, far from where their parents or guardians have been detained.

Teodora Martínez Salvador, 32, said she was “overjoyed” to hear about Trump’s executive order — but that she now wanted to be reunited quickly with her 15-year-old son.

“I need to hear his voice,” she said. ”There are many desperate mothers here.”

Patricia Yamileth Aragón, 41, of Honduras, said she hasn’t been able to speak with her daughter since June 14.

“It’s very cruel,” she said. “The hardest part is not being with our children.”

The Department of Homeland Security has said that 500 children have been reunited with parents since May. The agency told The Associated Press it wants to create a centralized process at the Port Isabel Detention Center to reunite all parents with children. The process in place now is daunting.

Parents are given a number to call but access to phones while in custody has been difficult. They must provide identifying information that matches with information documented by border officials who relay it to the Office of Refugee Resettlement (ORR), a division of the Department of Health and Human Services.

ORR can verify the child is in their custody but is prohibited from revealing the exact facility where the child is. That information is given to a caseworker who then must contact the parents or their attorney. John Sandweg, a former director of Immigration and Customs Enforcement, told MSNBC that separations sometimes are permanent because the parents are deported before finding their children.

Andrea Beatriz Vives Ruiz, 26, is from El Salvador. She is one of the more fortunate ones. She found her 9-year-old daughter in a shelter in Michigan after contacting other relatives.

She had this message for Trump: “Please give me the opportunity to stay here, to be here.”

“I’m too scared to return to my country,” she said. “I just want to be together with my daughter again.”

NBC News reporter Gabe Gutierrez and NBC News producer Bianca Seward reported from McAllen, Texas. NBC News reporter Suzanne Gamboa contributed from Austin, Texas.

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Suzanne Gamboa contributed.